1. Field of the Invention
The present invention relates to apparatus of the type sometimes called "fish locators" for determining the depth of certain temperature layers or strata in ponds, lakes, etc., in which fish of certain kinds are known to preferentially congregate, and more particularly to improved battery-operated fish locator apparatus which are self-compensating for changes in battery voltage due to aging and thus do not require to be manually adjusted to compensate for battery aging.
2. Description of the Prior Art
Fish locators in which the translator unit comprises a bridge circuit and a meter of the D'Arsonval type for indicating the temperature range of the water layer or stratum in which the temperature sensing element is located are well known in the prior art. As is well known, however, such bridge circuit arrangements are sensitive to variations in supply voltage. Thus, these prior art fish locator devices require to be manually adjusted to compensate for changes in the voltage of their batteries due to aging, and are provided with at least two potentiometers which the user must manually adjust in order to keep the meter readings accurate. Further, the user of these prior art fish locator devices is required to provide at least two baths of suitable temperature in which to successively immerse the temperature sensing element during manual compensation, and sometimes as many as five such baths. Yet further, the control means for these compensating potentiometers are located inside the cases of the prior art translator units, which must be opened during the manual compensating operations. Thus, these prior art fish locator devices are subject to problems brought about by the exposure of the translator circuit to moisture, and can be sealed against the entrance of moisture only with considerable difficulty and at considerable expense. Also, the D'Arsonval-type meters used in these prior art fish locator devices are inherently delicate and fragile and are subject to being rendered inaccurate or completely inoperative by the rough handling to which all fish tackle is sometimes subjected when in use or being carried in a tackle box or the like.